这个词是什么意思？
An extra-embryonic membranous sac derived from the YOLK SAC of REPTILES; BIRDS; and MAMMALS. It lies between two other extra-embryonic membranes, the AMNION and the CHORION. The allantois serves to store urinary wastes and mediate exchange of gas and nutrients for the developing embryo.
中文名称索引；定义为 MeSH 英文原文，尚未逐条译审。MESH:D000482 · MeSH 2026。
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